This grammar is difficult to adapt to ordered choice, having 4 possible variants that mostly define different languages from each other and from the "same" gram

This grammar is difficult to adapt to ordered choice, having 4 possible variants that mostly define different languages from each other and from the "same" grammar with traditional parsing. It's a formally very different problem from spontaneously and arbitrarily disambiguating an ambiguous grammar, but in practice it causes the same kind of suffering and it's likely to be a more common issue.